JP2022000516A - Process for polymerizing olefins in gas-phase - Google Patents

Abstract

To provide a polymerization process whereby: in a fluidized-bed reactor for the gas-phase polymerization process of olefins, in particular a multizone circulating reactor, it is possible to make easy control of a gas flow rate while maintaining the same pressure differential across a centrifugal compressor of a recycle line of a reaction gas, or to make changes in the pressure differential across the compressor while maintaining the same gas flow rate.SOLUTION: A gas-phase polymerization reactor for gas-phase polymerization of olefins comprises at least one polymerization zone which is equipped with a recycle line for withdrawing reaction gas from the reactor, leading the reaction gas through a heat-exchanger for cooling and feeding the reaction gas back to the reactor, wherein the recycle line is equipped with the heat-exchanger, a centrifugal compressor comprising variable guide vanes, and a butterfly valve, and process for preparing an olefin polymer in the gas-phase polymerization reactor.SELECTED DRAWING: None

Description

The present disclosure provides a gas phase polymerization reactor for gas phase polymerization of olefins and a process for producing an olefin polymer in the gas phase polymerization reactor. In this disclosure, in particular, vapor phase polymerization of olefins equipped with a recirculation line that draws the reaction gas from the reactor, induces the reaction gas through a cooling heat exchanger, and supplies the reaction gas back to the reactor. Provides a gas phase polymerization reactor for.

The vapor phase polymerization step is an economical step for the polymerization of olefins, such as homopolymerization of ethylene or propylene or copolymerization of ethylene or propylene with other olefins. Suitable reactors for performing such gas phase polymerization are, for example, fluidized bed reactors, stirred gas phase reactors or multizone circulating reactors with two different interconnected gas phase polymerization zones. It is a cyclic reactor). These steps are generally carried out in a gas phase comprising monomers and comonomer, often further including a polymerization diluent as a molecular weight modifier or a low molecular weight reaction product, eg, nitrogen or alkanes, or other gaseous components such as hydrogen. Will be done. The resulting product is a solid polyolefin particle generally formed by a polymerization catalyst system containing fine granular catalyst solids.

The olefin vapor phase polymerization process is characterized in that a large amount of gas is withdrawn from the reaction zone, passes through a heat exchanger to remove heat of polymerization, and then returned to the polymerization zone. In the fluidized bed reactor, the returned reaction gas further serves to keep the polyolefin particles in a fluidized state. In a multi-zone circulation reactor, circulation between the reactor zones is carried out by the returned reaction gas. To drive all these processes, the reaction gas recirculation line is usually fitted with a centrifugal compressor.

Centrifugal compressors are usually provided at the gas inlet of the compressor and are provided with a guide vane that directs the gas flow upwards on the centrifugal impeller. Such a guide vane may be a fixed guide vane, or the guide vane is variable. If a variable guide vane is installed, the gas suction angle of the compressor can also be changed by changing the position of the guide vane. As a result of such changes, the gas flow rate affected by the centrifugal compressor can change. However, such a change affects not only the gas flow rate but also the front-rear differential pressure in the compressor.

For example, WO 98/54231 A1 is a polymerization process of one or more α-olefins in a fluidized bed reactor in which a circulating gas valve or compressor inlet guide vane is used to control the temperature of the fluidized bed. The polymerization process used to manipulate the circulating gas flow rate is disclosed. However, in any case, such changes affect not only the gas flow rate but also the pressure of the recirculated gas.

In order for the polymerization conditions to be applicable in all situations, it is nevertheless necessary to regulate the fluidized gas flow independently of the differential pressure.

Therefore, to provide a polymerization process capable of easily manipulating the gas flow rate while keeping the front-rear differential pressure of the compressor constant, or changing the front-rear differential pressure of the compressor while keeping the gas flow rate constant. Is required.

The present disclosure is a gas phase polymerization reactor for vapor phase polymerization of olefins, in which a reaction gas is withdrawn from the reactor, the reaction gas is induced via a cooling heat exchanger, and the reaction gas is transferred to the reactor. The recirculation line comprises at least one polymerization zone to which the recirculation line is attached, the recirculation line is equipped with a centrifugal compressor equipped with a heat exchanger and a variable guide vane, and a butterfly valve, said variable. The guide vanes are located upstream of the centrifugal compressor and the butterfly valve is located downstream of the centrifugal compressor to provide a gas phase polymerization reactor.

In some embodiments, the recirculation line has one or more sidelines, which branch off from the recirculation line at a position between the centrifugal compressor and the butterfly valve and one or more sidelines. Is equipped with a control valve to control the flow rate of the branched recirculated gas in the sideline.

In some embodiments, the butterfly valve comprises a rotating disk having an area smaller than the cross section of the recirculation line at the position of the butterfly valve.

In some embodiments, the butterfly valve is located downstream of the heat exchanger.

In some embodiments, the centrifugal compressor is located upstream of the heat exchanger.

In some embodiments, the recirculation line is further equipped with a cyclone upstream of the heat exchanger and centrifugal compressor.

In some embodiments, the reactor is a fluidized bed reactor.

In some embodiments, the reactor is a multi-zone circulating reactor, where one polymerization zone is an ascending tube, where growing polyolefin particles flow upward under fast fluidization or transport conditions. , And the other polymerization zone is the descending tube, where the growing polyolefin particles flow downward in a densified form, the ascending tube and the descending tube are interconnected, and the polyolefin particles leaving the ascending tube are the descending tube. The polyolefin particles that enter and exit the descending tube enter the ascending tube and thus the circulation of the polyolefin particles through the ascending and descending tubes is established.

In some embodiments, the reactor is part of a reactor cascade.

In some embodiments, the reactor cascade comprises a first gas phase reactor and a subsequent second gas phase reactor, a sideline branching from the recirculation line of the second gas phase reactor. Is a transport line for sending the polyolefin particles from the first gas phase reactor to the second gas phase reactor.

In some embodiments, the present disclosure homopolymerizes an olefin at a temperature of 20-200 ° C. and a pressure of 0.5-10 MPa in the presence of a polymerization catalyst, or polymerizes an olefin with one or more other olefins. Provided is a process for producing an olefin polymer, which comprises copolymerizing, wherein the polymerization is carried out in the gas phase polymerization reactor according to any one of claims 1 to 10.

In some embodiments, the polymerization is carried out by a predetermined differential pressure in a centrifugal compressor and the change in recirculation gas flow rate is carried out by changing both the position of the guide vane and the position of the butterfly valve. ..

In some embodiments, the recirculation line has one or more sidelines, the sideline branching off from the recirculation line at a position between the centrifugal compressor and the butterfly valve and one or more sides. The line is fitted with a control valve to control the flow rate of the branched recirculation gas in the sideline, and the pressure of one or more sidelines upstream of the control valve is the recirculation line downstream of the butterfly valve. It is 0.01 MPa to 0.2 MPa higher than the pressure of.

In some embodiments, the polymerization is a homopolymerization of ethylene or a copolymerization of ethylene with one or more other olefins selected from the group consisting of 1-butene, 1-hexene and 1-octene. Alternatively, the polymerization is homopolymerization of propylene or copolymerization of propylene with one or more other olefins selected from the group consisting of ethylene, 1-butene, and 1-hexene.

In some embodiments, the polyolefin is a high density polyethylene having a density of 0.945 to 965 g / cm ^{3 as measured by ISO 1183 at 23 ° C.}

FIG. 1 schematically shows a fluidized bed reactor for carrying out the process of the present disclosure. FIG. 2 schematically shows a multi-zone circulation reactor for carrying out the process of the present disclosure. FIG. 3 schematically shows a cascade of two serially connected gas phase reactors for carrying out the process of the present disclosure.

The present disclosure is a gas phase polymerization reactor for gas phase polymerization of olefins, in which a reaction gas is withdrawn from the reactor, the reaction gas is induced through a cooling heat exchanger, and the reaction gas is transferred to the reactor. The recirculation line comprises at least one polymerization zone to which a recirculation line is attached and the recirculation line is provided with a gas phase polymerization reactor to which a centrifugal compressor and a heat exchanger are attached. Such reactors can be fluidized bed reactors, agitated gas phase reactors or multi-zone circulating reactors with two different interconnected gas phase polymerization zones. Reactors of these types are generally known to those of skill in the art. The agitated gas phase reactor can be agitated horizontally or vertically, for example. Desirable gas phase polymerization reactors according to the present disclosure are fluidized bed reactors and multi-zone circulation reactors.

The fluidized bed reactor is a reaction gas mixture that is fed at the lower end of the reactor, under a gas distribution grid that normally has the function of distributing the gas flow, and the gas is taken out again at the top of the fluidized bed reactor. A reactor in which polymerization occurs in a bed of polyolefin particles that are kept in a fluidized state. The reaction gas mixture is then returned to the lower end of the reactor via a recirculation line equipped with a centrifugal compressor and a heat exchanger to remove the heat of polymerization. The flow rate of the reaction gas mixture must first be high enough to fluidize the finely divided polymer bed present in the polymerization zone and secondly to effectively remove the heat of polymerization.

Multi-zone circulation reactors are described, for example, in WO 97/04015 A1 and WO 00/02929 A1 in which two interconnected polymerization zones, i.e., growing polyolefin particles, are fast. It has an ascending tube that flows upward under fluidization or transport conditions, and a descending tube in which growing polyolefin particles flow downward in a densified form under the action of gravity. The polyolefin particles exiting the ascending tube enter the descending tube, and the polyolefin particles exiting the descending tube are reintroduced into the ascending tube, thereby establishing a polymer circulation between the two polymerization zones and the polymer is these two. Alternately pass through the zone multiple times. In such a polymerization reactor, a solid / gas separator is placed above the descending tube to separate the polyolefin coming from the ascending tube from the reactive gaseous mixture. The growing polyolefin particles enter the descending tube and the separated reaction gas mixture in the ascending tube is continuously recirculated through the gas recirculation line into the polymerization reactor to one or more reintroduction points. Preferably, most of the recirculated gas is recirculated to the bottom of the riser. The recirculation line is equipped with a centrifugal compressor and a heat exchanger for removing heat of polymerization. Preferably, a line for feeding the catalyst or a line for feeding the polyolefin particles coming from the upstream reactor is arranged above the ascending tube and the polymer discharge system is located at the bottom of the descending tube. The introduction of make-up monomers, comonomer, hydrogen and / or inert components can occur at various points along the ascending and descending tubes.

The olefins that can be polymerized in the gas phase polymerization reactors of the present disclosure are, in particular, 1-olefins, i.e., hydrocarbons with terminal double bonds, and are not limited thereto. Non-polar olefin compounds are preferred. Particularly preferred 1-olefins are linear or branched _C 2 _-C 12-1-alkenes, especially ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1- branched _C 2 _-C 10 -1-alkenes such as linear _C 2 _-C 10 -1-alkenes such as decene or 4-methyl-1-pentene, 1,3-butadiene, 1,4-hexadiene or 1 , 7-Octadiene and other conjugated and non-conjugated diene. It is also possible to polymerize a mixture of various 1-olefins. Suitable olefins also include those in which the double bond is part of a cyclic structure capable of having one or more ring systems. Examples include cyclopentene, norbornene, tetracyclododecene or methylnorbornene or diene, such as 5-ethylidene-2-norbornene, norbornadiene or ethylnorbornadiene. It is also possible to polymerize a mixture of two or more olefins.

The gas phase polymerization reactor is particularly suitable for homopolymerization or copolymerization of ethylene or propylene, and is particularly preferable for homopolymerization or copolymerization of ethylene. Preferred comonomer in propylene polymerization is up to 40% by weight ethylene, 1-butene and / or 1-hexene, preferably 0.5% to 35% by weight ethylene, 1-butene and / or 1-hexene. As comonomers in the polymerization of ethylene, 20 wt% or less, more preferably 0.01 wt% to 15 wt%, in particular 0.05 wt% to 12 wt% of _C 3 _-C 8-1-alkenes, in particular 1-butene, It is preferred to use 1-pentene, 1-hexene and / or 1-octene. Polymerization in which ethylene is copolymerized with 0.1% by weight to 12% by weight of 1-hexene and / or 1-butene is particularly preferred.

The gas phase reactor according to the present disclosure is characterized in that the recirculation line is equipped with a centrifugal compressor equipped with a variable guide vane and a butterfly valve. The variable guide vane is located upstream of the centrifugal compressor and the butterfly valve is located downstream of the centrifugal compressor. The variable guide vanes of the compressor affect the gas flow rate and differential pressure by changing the gas suction angle of the compressor. Increasing the opening of the guide vanes increases both the gas flow rate and the differential pressure. Conversely, reducing the opening of the guide vanes reduces the gas flow rate and differential pressure. Another component that affects the gas flow rate and differential pressure in the recirculation line is the butterfly valve. The butterfly valve is a flow control device with a rotating disk installed in the passage. That is, this means that in the gas phase reactor of the present disclosure, a rotating disk is provided in the piping of the recirculation line. Increasing the opening of the butterfly valve increases the gas flow rate and reduces the differential pressure between the front and rear of the compressor. On the contrary, when the opening degree of the butterfly valve is reduced, the gas flow rate is reduced and the front-rear differential pressure of the compressor is increased. Therefore, by performing these adjustments at the same time, for example, it is possible to increase the flow rate of the fluidized gas while maintaining the same front-rear differential pressure in the compressor.

Using a butterfly valve as a means of controlling the flow rate of recirculation gas has the advantage that other types have a lower risk of device contamination compared to control valves and can establish a variable pressure drop in the recirculation line. There is. The butterfly valve is preferably configured to avoid sharp edges and corners within the butterfly valve, because small but still catalytically active particles entrained in the recirculating gas are in the butterfly valve. This is because the risk of adhering to a part of the particle can be minimized.

In a preferred embodiment according to the present disclosure, the butterfly valve comprises a rotating disk having an area smaller than the cross section of the recirculation line at the position of the butterfly valve. That is, when the butterfly valve is in the fully closed position, that is, when the rotating disk is arranged perpendicular to the gas flow, the gas flow is not completely shut off. Preferably, the area of the rotating disk is 90% to 99% of the cross section of the recirculation line at the position of the butterfly valve, and more preferably, the area of the rotating disk is 94% to 94% of the cross section of the recirculation line at the position of the butterfly valve. It is 98%. In a preferred embodiment of the butterfly valve, the rotating disc is circular and the non-blocking region of the recirculation line at the position of the butterfly valve in the closed position forms an annular gap around the rotating disc. In a preferred embodiment of the butterfly valve, the rotating disc is fixed in the center and rotates about an axis passing through the center of the rotating disc. Desirably, the butterfly valve is located at the position of the recirculation line where the recirculation line is not restricted.

In a preferred embodiment of the present disclosure, the recirculation line has one or more sidelines, the sideline branching off from the recirculation line at a position between the centrifugal compressor and the butterfly valve and one or more sides. The line is equipped with a control valve to control the flow rate of the branched recirculated gas in the side line. By designing the gas phase polymerization reactor according to the present disclosure, the side line can be operated by a predetermined front-rear differential pressure in the control valve independently of the recirculation gas flow rate. This allows the control valve to operate within a predetermined suitable control range. Preferably, such a suitable control range has a wide valve opening to minimize the risk of contamination by the accompanying particulates.

When controlling the flow of recirculated gas in the recirculation line only with the variable guide vanes without further control valve such as butterfly valve downstream of the branch position of the side line and the variable guide valve, for example, gas phase polymerization Reactor conditions that require a reduction in the flow rate of the recirculating gas in the recirculation line, such as the start of the compressor, result in a reduction in the anteroposterior differential pressure of the compressor and also induce a reduction in the anteroposterior differential pressure of the control valve. In order to maintain the intended gas flow through the sidelines, the control valve needs to be further opened, implying that the control valve may be out of the preferred control range, or the control valve design is different. In that case, if the flow rate of the recirculated gas is not reduced, the operation of the control valve will be out of the suitable control range. Further, in the configuration in which the recirculation gas branched to the side line is used as the transport gas or the carrier gas, the decrease in the front-rear differential pressure of the compressor causes the recirculation gas branched to the side line to act as the transport gas or the carrier gas. It can mean that the required differential pressure has not been reached, or at least not completely reached.

Another advantage of the gas phase polymerization reactors of the present disclosure is that partial contamination of the device in the gas circulation, such as partial contamination of the heat exchanger or partial contamination of the gas distribution grid, is a control valve in the sideline. It means that it can be easily compensated by a suitable wider opening of the butterfly valve without a change in the anteroposterior differential pressure. In the absence of a control valve, such as a butterfly valve downstream of the sideline branch, an opening in the compressor guide vanes may be required, which results in higher pressure downstream of the compressor, which results in higher pressure. It implies the risk that the control valve may go out of the preferred control range.

Heat exchangers can be placed at various points on the recirculation line. It is possible to install a heat exchanger upstream of the variable guide vanes and centrifugal compressor, the heat exchanger may be located between the centrifugal compressor and the butterfly valve, with the heat exchanger downstream of the butterfly valve. It may be installed. In the preferred embodiment of the present disclosure, the butterfly valve is located downstream of the heat exchanger.

Preferably, the centrifugal compressor is located upstream of the heat exchanger.

In a preferred embodiment of the present disclosure, the recirculation line is further fitted with a cyclone upstream of the centrifugal compressor and heat exchanger.

In a preferred embodiment of the present disclosure, the gas phase polymerization reactor is a fluidized bed reactor with a circulation loop connected to the gas distribution grid to recirculate the polyolefin particles from the gas distribution grid to the upper region of the fluidized bed reactor. Is. The carrier gas for transporting the polyolefin particles via the circulation loop is the recirculation gas provided by the side line branching from the recirculation line. A fluidized bed reactor of this type is disclosed, for example, in WO 2007/071527 A1. The recirculation line is equipped with both a centrifugal compressor with variable guide vanes and a butterfly valve to provide a sufficiently high front-to-back differential pressure at the sidelines branching from the recirculation line to air transport polyolefin particles within the circulation loop. While maintaining, for example, it is possible to reduce the flow rate of the recirculated gas at the start stage to reduce the carry-over of fine particles.

FIG. 1 schematically shows a fluidized bed reactor for carrying out the process of the present disclosure.

The fluidized bed reactor (1) includes a fluidized bed (2) of polyolefin particles, a gas distribution grid (3) and a deceleration zone (4). The deceleration zone (4) generally has an increased diameter relative to the diameter of the fluidized bed portion of the reactor. The polyolefin bed is maintained in a fluidized state by an upward flow of gas supplied through a gas distribution grid (3) located at the bottom of the reactor (1). The gaseous flow of reaction gas exiting the upper part of the deceleration zone (4) via the recirculation line (5) is compressed by a centrifugal compressor (6) containing a variable guide vane (7) and heat exchanger (8). After being transferred to and cooled here, it is recirculated to the bottom of the fluidized bed reactor (1) at a point below the gas distribution grid (3) at position (9). The recirculation line (5) further comprises a butterfly valve (10) downstream of the heat exchanger (8). The makeup monomer, molecular weight modifier, and optional inert gas can be supplied to the reactor (1) at various positions, for example, via the line (11) upstream of the compressor (6). In general, the catalyst is preferably supplied to the reactor (1) via a line (12) located below the fluidized bed (2).

The fluidized bed reactor (1) is provided with continuous air recirculation of the polyolefin particles by a circulation loop (13) connecting the gas distribution grid (3) to the upper region of the fluidized bed reactor (1). The circulation loop (13) includes a settling tube (14) integrated with the top opening in the gas distribution grid (3) and preferably arranged substantially vertically. The settling tube (14) has a large diameter section (14a) and a small diameter section (14b). The gas distribution grid (3) has a conical shape such that the downward slope towards the settling tube (14) facilitates the entry of polyolefin particles into the settling tube (14) by gravity. The upper opening of the settling pipe (14) is preferably located at the center of the gas distribution grid (3). The lower part of the settling tube (14) is connected to an air transport tube (15) having the function of reintroducing the polyolefin particles into the fluidized bed reactor (1). The outlet of the air transport pipe (15) is preferably located above the polymer floor (2) and below the deceleration region (4).

The discharge of the polyolefin particles from the fluidized bed reactor (1) is performed through the discharge conduit (16) attached to the large diameter portion (14a) of the settling pipe. The control valve (17) is located in the discharge conduit (16) in close proximity to the settling pipe (14) in order to regulate the flow rate of the polyolefin particles discharged from the fluidized bed reactor (1) to the discharge conduit (16). Will be installed. The discharge of the polyolefin particles is carried out continuously, and the opening degree of the control valve (17) is adjusted so as to keep the level of the polyolefin particles in the fluidized bed reactor (1) constant.

The control valve (17) is positioned according to the limitation of the settling pipe (14) existing between the large diameter portion (14a) and the small diameter portion (14b).

The polyolefin particles that are not discharged through the discharge conduit (16) are recirculated to the upper region of the fluidized bed reactor (1) by the circulation loop (13).

The carrier gas for transporting the polyolefin particles through the air transport pipe (15) is taken out from the gas recirculation lines at the downstream points of the compressor (6) and the upstream points of the heat exchanger (8), thereby. Utilize the pressure loss present through the heat exchanger (8), butterfly valve (10), distribution grid (3), and polymer bed (2). The carrier gas is mainly supplied via the line (18) at the inlet of the transport pipe (15). The flow rate control of the polyolefin particles recirculated through the circulation loop (13) is performed by the control valves (19) and (20) that regulate the flow rate of the carrier gas flowing into the transport pipe (15).

When starting a fluidized bed reactor according to the present disclosure, the recirculation gas rate shall be reduced at the start stage and the same front-rear differential pressure in the compressor shall be maintained as compared with the recirculation gas rate in steady state operation. Is possible. This can reduce the carryover of the fine powder at the start-up stage and ensure good circulation of the polyolefin particles through the air transport pipe by supplying a sufficient amount of carrier gas.

In another preferred embodiment of the present disclosure, the gas phase polymerization reactor is a multi-zone circulation reactor comprising a down tube with a throttle valve at the bottom. This valve is used to control the flow of polyolefin growing from the descending tube to the ascending tube. The throttle valve is preferably a mechanical valve such as a simple or double butterfly valve or a ball valve. A gas stream, sometimes referred to as an "input gas," is supplied to the bottom of the down tube at one or more positions directly above the valve to facilitate the flow of growing polyolefin particles through the valve. The velocity of the polyolefin particles in the descending tube can be adjusted by varying the opening of the valve and / or by varying the flow rate of the input gas. An additional gas stream, sometimes referred to as "carrying gas," is part of the multi-zone circulation reactor that connects the down tube to the up tube to carry polyolefin particles from the bottom of the down tube to the up tube, below the down tube. Is supplied to. Not only the carrier gas but also the input gas is the recirculation gas provided by the side line branching from the recirculation line. A multi-zone circulation reactor of this type is disclosed, for example, in International Publication No. WO2012 / 031986 A1. The recirculation line can be equipped with a centrifugal compressor containing a variable guide vane and a butterfly valve, for example, to reduce the flow rate of the recirculation gas at the start stage to reduce the carryover of fine particles, and the polyolefin in the descending tube. A sufficiently high front-to-back differential pressure in the sideline branching from the recirculation line to provide sufficient input and transfer gas to control the flow of particles and the transport of polyolefin particles from the descending tube to the ascending tube. It is possible to maintain.

FIG. 2 schematically shows a multi-zone circulation reactor for carrying out the process of the present disclosure.

The multi-zone circulating reactor (51) includes an ascending tube (52) as the first reactor zone and a descending tube (53) as the second reactor zone, with growing polyolefin particles repeating these. pass. In the riser tube (52), the polyolefin particles flow upward along the direction of the arrow (54) under high speed fluidization conditions. In the descending tube (53), the polyolefin particles flow downward along the direction of the arrow (55) under the action of gravity. The ascending pipe (52) and the descending pipe (53) are appropriately interconnected by the interconnected bending portions (56) and (57).

After flowing through the riser tube (52), the polyolefin particles and the reaction gas mixture exit the riser tube (52) and are carried into the solid / gas separation zone (58). Such solid / gas separation can be performed using conventional separation means such as, for example, a centrifuge such as a cyclone. From the separation zone (58), the polyolefin particles enter the descending tube (53).

The reaction gas mixture leaving the separation zone (58) is elevated by a recirculation line (59) equipped with a centrifugal compressor (60) containing a variable guide vane (61) and a heat exchanger (62). Recirculate to. The recirculation line (59) further includes a butterfly valve (63) downstream of the heat exchanger (62). A recirculation line (59) is separated between the compressor (60) and the heat exchanger (62), and the gaseous mixture is split into two separate streams: the line (64) is the recirculation gas. A portion of the gas is transported to the bottom of the riser tube (52) through a heat exchanger (62) and a butterfly valve (63), in which high speed fluidization conditions are established, while the line (65) is re-released. Another portion of the circulating gas is carried to the interconnect bent portion (57). A control valve (66) is attached to the line (65) in order to control the flow rate of the conveyed gas to the interconnect bend (57) via the line (65).

The suspension of the solid catalyst component is supplied to the catalyst injection point (68) of the multi-zone circulation reactor (51) via the line (67), or the multi-zone circulation reactor (51) is a gas phase reactor. When acting as a downstream reactor in the cascade, the flow of polyolefin particles growing from the pre-arranged gas phase reactor is fed through the line (67) to the polymer injection point (68). The polyolefin particles obtained in the multi-zone circulation reactor (51) are continuously discharged from the bottom of the descending pipe (53) via the discharge pipe (69).

A portion of the gaseous mixture exiting the separation zone (58) exits the recirculation line (59) after passing through the compressor (60) and is fed through the line (70) to the heat exchanger (71). Here, the monomer and the selective inert gas are cooled to a temperature at which they partially condense. The separation container (72) is located downstream of the heat exchanger (71). The separated liquid is drawn from the separation vessel (72) via the line (73) and supplied by the pump (75) through the line (74) to the descending pipe (53) to the ascending pipe (52). Creates a barrier to prevent the reaction gas mixture from entering the descending tube (53). The gaseous mixture obtained as a gas phase in the separation vessel (72) is recirculated through the line (76) to the recirculation line (59). Makeup monomers, makeup comonomers and optionally inert gas and / or process additives can be further introduced into the recirculation line (59) via the line (77).

A butterfly at the bottom of the descending tube (53) has an adjustable opening for regulating the flow of polyolefin particles from the descending tube (53) through the interconnected bend (57) to the ascending tube (52). A valve (78) is provided. At the top of the butterfly valve (78), the amount of the recirculated gas mixture coming from the recirculation line (59) through the line (79) is introduced into the down pipe (53) as input gas and through the butterfly valve (78). Promotes the flow of polyolefin particles. A control valve (80) is attached to the line (79) to control the flow rate of the input gas.

In a more preferred embodiment of the present disclosure, the gas phase polymerization reactor is part of a reactor cascade. Desirably, the reactor cascade has a first gas phase reactor followed by a second gas phase reactor, with sidelines branching from the recirculation line of the second gas phase reactor being polyolefin particles. Is a transfer line for sending from the first gas phase reactor to the second gas phase reactor. Then, the transfer of the polyolefin particles from the first gas phase reactor to the second gas phase reactor is performed by a gas flow, and occasionally the recirculated gas of the second gas phase reactor is "pickup gas". Called. Such a type of reactor cascade is disclosed, for example, in WO 2013/0853548 A1. By installing both a centrifugal compressor with a variable guide vane and a butterfly valve in the recirculation line of the second gas phase reactor, for example, at the start-up stage, the flow rate of the recirculation gas is reduced to reduce the carryover of fine powder. A sufficient amount of pick-up gas can be provided and sufficient to air transport the polyolefin particles from the first gas phase reactor of the reactor cascade to the second gas phase reactor of the reactor cascade. Sufficient high anteroposterior differential pressure in the sidelines branching from the recirculation line to clearly empty the transport line when the discharge of polyolefin particles from the first gas phase reactor of the reactor cascade is interrupted or terminated. It is possible to maintain.

FIG. 3 schematically shows a cascade of two serially connected gas phase reactors for carrying out the process of the present disclosure.

The fluidized bed reactor (101) shown in FIG. 3 is similar to the fluidized bed reactor 1 shown in FIG. 1, and the multi-zone circulating reactor (151) shown in FIG. 3 is the multi-zone shown in FIG. It is similar to the circulating reactor (51).

The fluidized bed reactor (101) differs from the fluidized bed reactor (1) in that the fluidized bed reactor (101) does not include a circulation loop (13). Instead, the sedimentation pipe (114) is closed at the lower end by a discharge valve (117), which is preferably a segment ball valve. During the operation of the fluidized bed reactor (101), the layer of polyolefin particles contained in the settling tube (114) enters the settling tube (114) at the upper opening integrated with the gas distribution grid (3). Move from the top to the bottom of. The discharge valve (117) is arranged on a line (181) that branches from the line (65) of the multi-zone circulation reactor (151) and carries a part of the recirculated gas of the multi-zone circulation reactor (151). .. A control valve (182) is attached to the line (181) in order to control the flow rate of the pickup gas through the line (181). The polyolefin particles that have passed through the discharge valve (117) enter the line (181) and are transported by pickup gas to the multi-zone circulation reactor (151) where the polyolefin particles enter at position (182).

The settling tube (114) further comprises a line (121). This line is preferably located near the lower end of the settling tube (114) and is intended to feed the bed of polyolefin particles in the settling tube (114) with a fluid that guides the fluid in the upper stream. In this way, the reaction gas mixture of the fluidized bed reactor (101) is prevented from being mixed into the line (181) and the multi-zone circulation reactor (151). The flow of fluid in the line (121) is controlled by the control valve (122). In the fluidized bed reactor (101) to compensate for a portion of the fluid that has flowed into the settling tube (114) via the line (121) that enters the fluidized bed reactor (101) through the settling pipe (114). A part of the reaction gas of the reactor must be discharged. This is done via a recovery line (124) branching from the recirculation line (5) between the centrifugal compressor (6) and the heat exchanger (8). The gas flow through the recovery line (124) is controlled by the control valve (125). The reaction gas extracted via the line (124) is preferably conveyed to a work-up section (not shown in FIG. 3).

The present disclosure comprises homopolymerizing an olefin at a temperature of 20-200 ° C. and a pressure of 0.5-10 MPa in the presence of a polymerization catalyst, or copolymerizing an olefin with one or more other olefins. Further providing a process for producing the polymer, the polymerization is carried out in the gas phase polymerization reactor as described above.

Preferably, the polymerization is homopolymerization of ethylene or copolymerization of ethylene with one or more other olefins selected from the group consisting of 1-butene, 1-hexene and 1-octene, or the polymerization is , A homopolymerization of propylene or a copolymerization of propylene with one or more other olefins selected from the group consisting of ethylene, 1-butene, and 1-hexene. In a preferred embodiment, the resulting polyolefin is a high density polyethylene having ^{a density of 0.945 to 965 g / cm 3 as measured by ISO 1183 at 23 ° C.}

The gas phase polymerization reactors of the present disclosure may operate at pressures of 0.5 MPa to 10 MPa, preferably 1.0 MPa to 8 MPa, particularly 1.5 MPa to 4 MPa, all of which are provided in the present disclosure. It should be understood that the pressure of is an absolute pressure, that is, a pressure having a dimension of MPa (abs). The polymerization is preferably carried out at a temperature of 30 ° C. to 160 ° C., particularly preferably 65 ° C. to 125 ° C., and the temperature near the upper limit of the above range is optimal for producing a relatively high density ethylene copolymer. The temperature near the lower limit of the above range is optimal for the production of low density ethylene copolymers.

Polymerization in the gas phase polymerization reactor can also be carried out in condensed or supercondensed mode, where a portion of the circulating reaction gas mixture is cooled below the dew point and further vaporization enthalpy is added to cool the reaction gas. To be utilized, return to the reactor separately as a liquid phase and a gas phase, or together as a two-phase mixture. When operating in a condensed or supercondensed mode, the gas phase polymerization reactor is preferably a fluidized bed reactor.

In a preferred embodiment of the present disclosure, the polymerization is an inert gas such as nitrogen or an alkane with 1-10 carbon atoms such as methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane or n-hexane. Or performed in the presence of a mixture of these. Nitrogen or propane as the inert gas is preferably used in combination with additional alkanes, if appropriate. In a particularly preferred embodiment of the present disclosure, the polymerization in the presence of C ₃ -C ₅ alkanes as a polymerization diluent, and most preferably in the presence of propane is particularly performed in the case of homopolymerization or copolymerization of ethylene To. The reaction gas mixture in the reactor further comprises the olefin to be polymerized, i.e. the main monomer and one or more selective comonomer. In a preferred embodiment of the present disclosure, the reaction gas mixture has an inert component content of 30-99% by volume, more preferably 40-95% by volume, particularly 45-85% by volume. In another preferred embodiment of the present disclosure, the Inactive Diluent is not added at all or is added in trace amounts, especially if the main monomer is propylene. The reaction gas mixture can further contain additional components such as molecular weight modifiers such as hydrogen or antistatic agents. The components of the reaction gas mixture may be supplied to the gas phase polymerization reactor, gaseous to the recirculation line, or as a liquid that vaporizes in the reactor or recirculation line after being supplied.

Polymerization of olefins can be carried out using all conventional olefin polymerization catalysts. This means that the polymerization can be carried out using a chromium oxide based Philips catalyst, a Ziegler or Ziegler-Natta catalyst, or a single site catalyst. For the purposes of the present disclosure, single-site catalysts are catalysts based on chemically homogeneous transition metal coordination compounds. In addition, mixtures of two or more of these catalysts can be used for the polymerization of olefins. Such mixed catalysts are often referred to as hybrid catalysts. The production and use of these catalysts for olefin polymerization are generally known.

Preferred catalysts are of the Ziegler type, preferably containing titanium or vanadium compounds, magnesium compounds and optionally electron donor compounds and / or particulate inorganic oxides as carrier materials.

Ziegler-type catalysts are usually polymerized in the presence of co-catalysts. Preferred co-catalysts are organometallic compounds of Group 1, 2, 12, 13 or 14 of the Periodic Table of the Elements, particularly organometallic compounds of Group 13 metals and organoaluminum compounds in particular. Preferred co-catalysts are, for example, organometallic alkyls, organometallic alkoxides, or organometallic halides.

Preferred organometallic compounds include lithium alkyl, magnesium or zinc alkyl, magnesium alkyl halides, aluminum alkyl, silicon alkyl, silicon alkoxides and silicon alkyl halides. More preferably, the organometallic compound contains aluminum alkyl and magnesium alkyl. More preferably, the organometallic compound comprises an aluminum alkyl, most preferably a trialkylaluminum compound or a compound of this type in which the alkyl group is substituted with a halogen atom, for example chlorine or bromine. Examples of such aluminum alkyl are trimethylaluminum, triethylaluminum, tri-isobutylaluminum, tri-n-hexylaluminum or diethylaluminum chloride or mixtures thereof.

A preferred catalyst is also a Phillips-type chromium catalyst, which preferably applies a chromium compound to an inorganic carrier and then activates the resulting catalyst precursor at temperatures in the 350-1000 ° C range, with atoms lower than 6. Manufactured by converting the valence-existing chromium into a hexavalent state. In addition to chromium, additional elements such as magnesium, calcium, boron, aluminum, phosphorus, titanium, vanadium, zirconium and zinc can also be used. It is particularly preferred to use titanium, zirconium or zinc. Combinations of the above elements are also possible. The catalyst precursor can be doped with fluoride before or during activation. Further, as a carrier for a Phillips type catalyst known to those skilled in the art, aluminum oxide, silicon dioxide (silica gel), titanium dioxide, zirconium dioxide or a mixed oxide or cogel thereof, or aluminum phosphate may be mentioned. More suitable carrier materials can be obtained, for example, by modifying the pore surface area using compounds of elemental elements such as boron, aluminum, silicon or phosphorus. It is preferable to use silica gel. Spherical or granular silica gel is preferred, and spherical silica gel can also be spray dried. The activated chromium catalyst can then be prepolymerized or prereduced. Pre-reduction is generally carried out in an activator at 250 ° C. to 500 ° C., preferably 300 ° C. to 400 ° C. with cobalt or with hydrogen.

In a preferred embodiment of the present disclosure, the polymerization is carried out by a predetermined anteroposterior differential pressure in a centrifugal compressor, and the change in the recirculation gas flow rate is carried out by changing both the position of the guide vane and the position of the butterfly valve.

Desirably, the recirculation line of the gas phase reactor has one or more sidelines, which branch off from the recirculation line at the position between the centrifugal compressor and the butterfly valve and one or more sidelines. Is equipped with a control valve to control the flow rate of the branched recirculation gas in the sideline, and in the polymerization, the pressure of one or more sidelines upstream of the control valve recirculates downstream of the butterfly valve. The pressure is 0.01 MPa to 0.2 MPa higher than the pressure of the line, preferably 0.02 MPa to 0.1 MPa higher than the pressure of the recirculation line downstream of the butterfly valve.

In another desirable embodiment of the present disclosure, the polymerization is polymerization in a gas phase reactor that is part of a cascade of polymerization reactors and one or more in other gas phase reactors of said polymerization reactor cascade. The polymerization can be the polymerization according to the present disclosure. A suitable combination of such polymerization reactors would be a fluidized bed reactor followed by a multi-zone circulation reactor followed by a multi-zone circulation reactor followed by a fluidized bed reactor and two or three flows. A cascade of bed reactors is provided, followed by one or two loop reactors followed by one or two fluidized bed reactors.

The melting flow rate MFR _{190 / 2.16} was measured according to DIN EN ISO 1133-1: 2012-03 at a temperature of 190 ° C. under a load of 2.16 kg.

Density was measured with a 2 mm thick compression molded plaque according to DIN EN ISO 1183-1: 2004, Method A (immersion). The compression molded plaques were produced with a defined thermal history: pressurized at 180 ° C., 20 MPa for 8 minutes, followed by crystallization in boiling water for 30 minutes.

Comparative Example A
Comparative Example A using a fluidized bed reactor having the configuration shown in FIG. 1, including a centrifugal compressor with a variable guide vane but without a butterfly valve attached to the downstream recirculation line of the heat exchanger. Phase polymerization was carried out. The design parameters of the fluidized bed reactor are as follows:
Reactor diameter: 4.0m
Circulation loop diameter: 0.2m
A conical fluidized grid with bottom vertices.
The fluidized bed reactor was designed to operate at a fluidization rate within the fluidized bed reactor at 0.9 m / s.

The Ziegler-Natta catalyst 1.2 kg / h produced according to Example 13 of WO2004 / 106388A1, which has an electron donor / Ti molar feed ratio of 8, is triisobutyl using 25 kg / h of liquid propane. Aluminum (TIBA), diethylaluminum chloride (DEAC) and tetrahydrofuran (THF) were also fed into the infused first stirring pre-contact vessel. The weight ratio of triisobutylaluminum to diethylaluminum chloride was 7: 1. The weight ratio of aluminum alkyl to solid catalyst was 10: 1. The weight ratio of aluminum alkyl to THF was 10: 1. The first preliminary contact vessel was maintained at 50 ° C. with a residence time of 10 minutes. The catalytic suspension of the first preliminary contact vessel was continuously transferred to the second stirring preliminary contact vessel, which was also operated at 50 ° C. with a residence time of 60 minutes. The activated catalyst suspension was then continuously charged into the fluidized bed reactor.

The production of polyethylene began using an empty reactor, a reactor that does not contain polyolefin particles. The fluidization rate in the fluidized bed reactor was 0.9 m / s. Twenty-four hours after the catalyst supply to the first preliminary contact vessel was started, the fluidized bed reactor was in a steady state. The fluidized bed reactor operated at an absolute pressure of 25 bar and a temperature of 80 ° C. The front-rear differential pressure of the centrifugal compressor was 0.2 MPa. The reaction gas had the following composition. : Ethylene: 24 mol%; 1-butene: 14 mol%; H ₂ : 5.5 mol%; ethane: 1 mol%; propane: 55.5 mol%. The plant throughput was 16 t / h, the productivity of the catalyst was 10,000 g of polyethylene / g of the catalyst, and the residence time was 2.8 hours.

The polyethylene produced had densities _{of MFR 190 / 2.16} and 0.9185 g / cm ³ at 0.95 g / 10 min.

After one day of steady state operation, the efficiency of the heat exchanger was observed to decrease slightly. Polymerization was terminated and the recirculation system was inspected. Polymer wall membranes were detected in the heat exchanger pipes and in the walls of the recirculation line upstream of the heat exchanger. Also, a small amount of chunks was observed in the heat exchanger at the top of the heat exchanger pipe.

Comparative Example B
After washing the polymerization reactor, the polymerization of Comparative Example A was repeated. However, the fluidized bed reactor was started at a fluidization rate in the fluidized bed reactor at 0.7 m / s to reduce carryover to the recirculation line. As a result, the differential pressure between the front and back of the centrifugal compressor became 0.1 MPa. After 12 hours of initiation, the circulation loop was occluded, indicating that inadequate circulation of polyolefin particles had occurred in the circulation loop.

Example 1
After washing the polymerization reactor, the polymerization of Comparative Example A was repeated, but only after the fluidized bed reactor was modified. The modified polymerization reactor has the configuration shown in FIG. 1 including a recirculation line, not only fitted with a centrifugal compressor with variable guide vanes, but also with a butterfly valve installed downstream of the heat exchanger. Had.

The fluidized bed reactor was started and operated at a fluidization rate of 0.75 m / s in the fluidized bed reactor, but because a butterfly valve that was partially closed was used, the differential pressure between the front and rear of the centrifugal compressor was It was 0.2 MPa. No blockage of the circulation loop was observed.

Polymerization continued for a week without blockage of the circulation loop or reactor effluent system. After that, the plant was closed according to the schedule. Subsequent inspection of the recirculation system showed clean recirculation lines and heat exchangers without any surface layer of polymer.

Claims (15)

A gas phase polymerization reactor for vapor phase polymerization of olefins, which draws a reaction gas from the reactor, induces the reaction gas through a cooling heat exchanger, and supplies the reaction gas to the reactor again. The recirculation line comprises at least one polymerization zone to which the circulation line is attached, and the recirculation line is equipped with a centrifugal compressor equipped with a heat exchanger and a variable guide vane, and a butterfly valve. A gas phase polymerization reactor located upstream of the centrifugal compressor, wherein the butterfly valve is located downstream of the centrifugal compressor. The recirculation line has one or more sidelines, the sideline branching from the recirculation line at a position between the centrifugal compressor and the butterfly valve, and one or more sidelines having a side. The reactor according to claim 1, wherein a control valve for controlling the flow rate of the branched recirculated gas in the line is attached. The reactor according to claim 1 or 2, wherein the butterfly valve is smaller than the cross section of the recirculation line at the position of the butterfly valve. The reactor according to any one of claims 1 to 3, wherein the butterfly valve is arranged downstream of the heat exchanger. The reactor according to any one of claims 1 to 4, wherein the centrifugal compressor is arranged upstream of the heat exchanger. The reactor according to any one of claims 1 to 5, wherein the recirculation line is further provided with a cyclone upstream of the heat exchanger and the centrifugal compressor. The reactor according to any one of claims 1 to 6, wherein the reactor is a fluidized bed reactor. The reactor is a multi-zone circulation reactor, where one polymerization zone is an ascending tube, where growing polyolefin particles flow upward under fast fluidization or transport conditions, and the other polymerization. The zone is the descending tube, where the growing polyolefin particles flow downward in a densified form, the ascending tube and the descending tube are interconnected, and the polyolefin particles leaving the ascending tube enter the descending tube and enter the descending tube. A multi-zone circulation reactor, wherein the polyolefin particles exiting the above tube enter the ascending tube and thus the circulation of the polyolefin particles through the ascending tube and the descending tube is established, according to any one of claims 1 to 6. The reactor described. The reactor according to any one of claims 1 to 8, wherein the reactor is a part of a reactor cascade. The reactor cascade has a first gas phase reactor and a subsequent second gas phase reactor, and a side line branching from the recirculation line of the second gas phase reactor contains polyolefin particles. The reactor according to claim 9, which is a transfer line for sending from the gas phase reactor 1 to the second gas phase reactor. A process for producing an olefin polymer comprising homopolymerizing an olefin at a temperature of 20-200 ° C. and a pressure of 0.5-10 MPa in the presence of a polymerization catalyst, or copolymerizing an olefin with one or more other olefins. The process in which the polymerization is carried out in the gas phase polymerization reactor according to any one of claims 1 to 10. The process of claim 11, wherein the polymerization is carried out at a predetermined differential pressure in a centrifugal compressor, and the change in the recirculating gas flow rate is carried out by changing both the position of the guide vane and the position of the butterfly valve. .. The recirculation line has one or more sidelines, the sideline branching off the recirculation line at a position between the centrifugal compressor and the butterfly valve, and the sideline to the one or more sidelines. A control valve is installed to control the flow rate of the branched recirculation gas in the line, and the pressure of one or more sidelines upstream of the control valve is higher than the pressure of the recirculation line downstream of the butterfly valve. The process according to claim 11 or 12, which is 0.01 MPa to 0.2 MPa higher. The polymerization is a homopolymerization of ethylene or a copolymerization of ethylene with one or more other olefins selected from the group consisting of 1-butene, 1-hexene and 1-octene, or the polymerization is The process according to any one of claims 11 to 13, wherein the homopolymerization of propylene or the copolymerization of propylene with one or more other olefins selected from the group consisting of ethylene, 1-butene, and 1-hexene. .. The process of claim 14, wherein the resulting polyolefin is a high density polyethylene having a density of 0.945 to 965 g / cm ^{3 as measured by ISO 1183 at 23 ° C.}

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